Determination of Colistin Susceptibility in Bacterial Isolates

Antibiotic resistance is of increasing concern within medicine and animal medicine. As part of the Society's continuing commitment to contributing to the discussions taking place in the wider industry, the following information is provided to members on colistin.

- Colistin is currently being used as the drug of last resort to treat some human infections, for example Pseudomonas aeruginosa respiratory infections in cystic fibrosis patients.

- This is leading to increased focus on this antimicrobial and its usage in veterinary medicine.

- Transferable resistance to colistin was recently first detected in E. coli from pigs in China and has subsequently been detected in E. coli from pigs in the UK as well as in E. coli frompigs, poultry and calves in Europe.

- The Pig Veterinary Society recently re-categorised colistin into class 3 of the PVS Prescribing Principles for Antimicrobials (Class 3 - only to be used when no other options are available and supported by laboratory sensitivity tests or in extreme circumstances when all else has failed).

- Standard disc diffusion testing is no longer considered sufficiently robust for determination of colistin susceptibility (colistin diffuses poorly in agar) and other methods must therefore be used.

- Appropriate methods for determining colistin susceptibility in relevant enteric bacteria such as E. coli and Salmonella are being introduced across APHA

- This is already in place at the Bury St Edmunds veterinary investigation centre which deals with samples submitted from two of the main areas of pig production (Thirsk and Bury St Edmunds regions).

- If you are submitting to a different APHA site, if colistin susceptibility is particularly required for enteric bacteria recovered from any species, please mark the submission form or contact your relevant veterinary investigation centre or external post-mortem provider to indicate that requirement.